This invention relates generally to blister strips used to deliver powdered medication, and more particularly to a system and method for accurately measuring the content contained in the blisters comprising a blister strip.
Powdered medication for use with Multi Dose Powder Inhalers (MDPI) is provided in blister strips comprised of one or more rows of blisters (indents made in an aluminum foil strip wherein each blister is filled with a metered amount of medication and the powder sealed within the blister by a composite lid foil).
A device is provided for the user that removes the lid foil, thus releasing the powder for use, so that the user can inhale the powdered medication. A variety of ailments can be treated in this manner, particularly asthma. Also, recent developments in antibiotic medications have proven MDPI to be an effective method of introducing the medication into a user""s system.
In any case, irrespective of the medical condition being treated, it is critical that each blister contain the correct metered dose of medication to ensure proper treatment of the ailment and protect the user from over-medication or under-medication.
Currently, to ensure that the correct metered dose is being dispensed in each blister, random strips from a production run are tested by weighing each strip, inserting a needle into the individual blisters one at a time, extracting the powder through suction and then re-weighing the strip. Not only is this method time consuming (a strip comprising 120 blisters can typically take up to one hour to test), but the method has within it inherent inaccuracies. For instance, if all the powder is not extracted from each blister, then the weight of the strip after the powder has supposedly been removed will be inaccurate. Moreover, because it is understood and accepted that powder residue is left behind within the blister, a percentage of residual powder is assumed and an additional weight based on that assumed percentage is automatically subtracted from the weight of the empty strip.
Accordingly, because it is essential that the powder medication be dispensed in the correct metered dose, it is essential that the powder contained in each blister be accurately measured to ensure proper dosage.
This invention results from the realization that a truly effective system and method for accurately measuring a dose of powdered medication contained in a blister for use in a metered dose powder inhaler can be achieved in which the powder filled blister is punched from a blister strip without breaking the blister, to prevent loss of powder weight, and the punched blister is weighed. A predetermined weight, representing the weight of an empty blister, is subtracted from the weight of the punched blister to determine the weight of the powder dose contained in the punched blister.
The invention results from the further realization that the correct size of a blister can be verified by measuring the maximum height of the blister and comparing it to a predetermined height to determine whether the blister is the correct size for receiving, and thus dispensing, a predetermined dose of medication.
The invention results still further from the realization that a blister can be accurately punched without breaking the blister. This is accomplished by monitoring the profile of the blister whereby the center of the blister is determined. The blister is advanced a predetermined distance based on the blister""s center to the punch such that the blister is accurately aligned beneath the punch. The foil strip or blister strip is then punched from the strip without breaking the blister.
This invention features a system for check-weighing a metered dose powder inhaler blister. The system comprises a guide adapted to receive a blister strip having at least one blister, a punch aligned with the guide for receiving the at least one blister, and an actuator engaging the punch for driving the punch toward the blister strip whereby the blister is punched from the blister strip. A balance adapted to receive the punched blister is provided for weighing the punched blister and generating a punched blister weight for the at least one blister.
In one embodiment of the present invention there can be a computer controller, responsive to the balance, for subtracting a predetermined weight from the punched blister weight. A drive assembly can be included, responsive to the blister strip, for advancing the at least one blister toward the punch. The drive assembly can include a drive wheel adapted to engage a first side of the blister strip for advancing the at least one blister toward the punch and a friction wheel adapted to engage a second side of the blister strip opposite the first side for urging the blister strip toward the friction wheel to ensure the friction wheel properly engages the blister strip. The drive assembly can include a stepper motor responsive to the computer controller for engaging the drive wheel to advance the at least one blister a predetermined distance toward the punch.
A sensor can be provided, aligned with the guide and responsive to the at least one blister, for detecting the profile of the at least one blister. The sensor can include an energy source for directing a beam of energy toward the blister strip and a detector for receiving a beam of reflected energy from the blister strip. The energy source can include a light source, which can be a laser. The guide can include a spring for urging the blister trip into the guide to ensure the profile of the blister is accurately detected. The guide can further include a hole through which the beam of energy passes to prevent a beam of reflected energy from being detected in the absence of a blister strip within the guide. The punch can include a clamp such as a stripper plate, responsive to the actuator, for holding the blister strip within the guide as the blister is being punched from the blister strip to ensure a clean punch. The punch can also include a contoured tip for seating the blister within the punch as the blister is being punched from the blister strip to ensure that the blister is not broken when punched, the tip engaging the blister strip at an oblique angle. The actuator can include a fluid driven actuator which can be an air cylinder.
The invention also features a method for weighing the content of a blister in a blister strip. The method includes punching a blister containing a metered content from a blister strip, weighing the punched blister to determine a punched blister weight and subtracting from the punched blister weight a predetermined weight and representing the weight of an empty blister to determine a weight representative of the metered content.
In one embodiment the step of punching can include punching the blister from the blister strip without breaking the blister. The method can also include the steps of punching a blank from the blister strip and weighing the blank to produce the predetermined weight. The method can also include the step of measuring the height of the blister prior to punching the blister and detecting the center of the blister to facilitate alignment of the blister for punching. The step of detecting the center can include calculating first and second slopes of respective first and second blister sides to generate a blister profile and detecting the midpoint, or center, of the blister profile which represents the center of the blister.
The invention further features a method for detecting defects in a blister strip blister. The method includes directing a beam of energy from an energy source toward a blister strip containing at least one blister, moving the blister strip in alignment with the beam of energy such that the at least one blister passes through the beam of energy, and receiving beams of reflected energy from the blister strip. The maximum height of the at least one blister is determined from the reflected beams of energy and compared to a predetermined height.
The invention features still further a method for aligning a blister strip blister with a punch. The method includes directing a beam of energy from an energy source toward a blister strip containing at least one blister, moving the blister strip toward a punch in alignment with the beam of energy such that the at least one blister passes through the beam of energy. Reflected beams of energy from the blister strip are received and the center of the blister is detected. The blister is moved, in response to the detected center, a predetermined distance toward the punch so that the blister is accurately aligned with the punch.
In one embodiment the step of detecting the center can include calculating first and second slopes of respective first and second sides of the blister to generate a blister profile and detecting the midpoint of the blister profile which represents the center f the blister. The step of detecting the center can also include detecting the maximum height of the blister.
Finally, the invention features a system for aligning a blister strip blister with a punch including an energy source for directing a beam of energy toward a blister strip containing at least one blister, a drive assembly for moving the blister strip in alignment with the beam of energy such that the at least one blister passes through the beam of energy and a detector for receiving beams of reflected energy from the blister strip. There are means for detecting the center of the at least one blister from the reflected beams of energy. The drive assembly, in response to the detected center, moves the blister a predetermined distance, the distance from the sensor to a punch, toward the punch so that the blister is aligned with the punch.
In one embodiment the means for detecting can include means, responsive to the detector, for calculating first and second slopes of respective first and second sides of the blister and generating a blister profile and means, responsive to the means for calculating, for determining the midpoint of the blister profile which represents the center of the blister. The means for detecting the center can include means, responsive to the detector, for detecting the maximum height of the blister which represents the center of the blister.
It is therefore an object of the present invention to provide a system and method that accurately and efficiently weighs the amount of powder contained in a blister strip blister.
It is a further object of the present invention to provide such a system and method that detects defects in a blister strip blister.
It is still a further object of this invention to provide such a system and method that accurately aligns a blister with a punch to punch the blister without breaking the blister.